METHODS OF SAMPLING THE BENTHOS
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B. Grab sampling
Grabs and other quantitative samplers are lowered vertically from
the drifting ship. For some purposes it may be necessary to anchor,
but if some precision is required over a number of hauls when in
FIG. 29. Lowering the Peteraen grab from a boom. Even in fairly calm weether the
greb may awing dengeroualy. (i'hoto: U. M. Grigg.)
deeper water it may be possible to drop a dan buoy to mark the position, steaming back to it between each haul, or as necessary.
Grabs like the Petersen grab may be worked through the trawl
gallows, and this may be possible with the van Veen if the gallows are
high enough. Alternatively, a boom or davit may be used, but thin
allows the grab a longer scope for swinging against the ship and
causing damage. We have found that it is easier to control a swinging
grab if it ha3 a frame which can easily be grasped (as in Holme's scoop-
225
B. Grab sampling
Grabs and other quantitative samplers are lowered vertically from
the drifting ship. For some purposes it may be necessary to anchor,
but if some precision is required over a number of hauls when in
FIG. 29. Lowering the Peteraen grab from a boom. Even in fairly calm weether the
greb may awing dengeroualy. (i'hoto: U. M. Grigg.)
deeper water it may be possible to drop a dan buoy to mark the position, steaming back to it between each haul, or as necessary.
Grabs like the Petersen grab may be worked through the trawl
gallows, and this may be possible with the van Veen if the gallows are
high enough. Alternatively, a boom or davit may be used, but thin
allows the grab a longer scope for swinging against the ship and
causing damage. We have found that it is easier to control a swinging
grab if it ha3 a frame which can easily be grasped (as in Holme's scoop-